Obviously it depends on how much time and effort you put into it. I'm personally loving golf since I started playing it, so I'm doing all I can to improve.
Been playing 2 years now (1 of which I joined a club and started to play to improve). I was playing every now and then last year, but this year (especially over the summer), I've been playing 9 holes during the week once and a full round of 18 at the weekend.
My stats are as follows:
October 2012: +28
March 2013: +24
August 2013: +24
September 2013: +19
October 2013: +16.7
Little chart below from the Howdidido.co.uk website that shows the changes recently:
The recent drop I put down to buying new equipment (having 4 wedges has helped my game a lot), working on my swing and actually practicing chipping and lots of putting.